In many typical communication systems, a characterization of the communication channel may be determined (e.g. estimated) and used to improve performance (e.g. capacity, throughput, error rate, etc.) of future communication (transmission and/or reception). Well known examples of such channel characterization include channel state information (CSI), channel quality indication (CQI), and channel impulse response estimates in general. Well known ways to apply the channel characterization include pre-coding (e.g. beam forming for multi-antenna systems such as multiple input multiple output (MIMO) systems, phase array systems, and massive MIMO systems).
In some applications, a first device transmitting to a second device over a communication channel uses a channel characterization produced by the second device to improve performance related to its transmission. The channel characterization may typically be conveyed from the second device to the first device through some kind of feed-back mechanism.
Example drawbacks of such an approach include increased signaling overhead, limited channel characterization accuracy (due to quantization of the information to be fed back), and delayed update of the applied channel characterization by the first device.
In some applications, if time division duplex (TDD) is used with transmission and reception at the same frequency, reciprocity may be assumed and a channel characterization produced by the first device may be used by the first device to improve performance related to its transmission, instead of a channel characterization produced by the second device. It is often assumed that TDD must be used for some systems to work efficiently. One example is fifth generation communication systems applying massive MIMO, where a TDD mode of operation is often selected at least partly due to the above mentioned feedback issues.
Example drawbacks of such an approach include increased buffering needs at the transmitter (due to the transmission interruptions inherent in TDD) and increased latency (also due to the transmission interruptions inherent in TDD). Other drawbacks of TDD include reduced throughput, slow update of the applied channel characterization, and inferior synchronization.
WO 2014/202156 A1 discloses a transceiver arrangement for a fixed point-to-point radio link. The transceiver arrangement comprising a transceiver connected to a first antenna and to a second antenna. The transceiver being arranged to transmit a first transmit signal via the first antenna in a first frequency band, the transceiver also being arranged to receive a first receive signal via the first antenna in a second frequency band, the transceiver further being arranged to transmit a second transmit signal via the second antenna in the second frequency band, the transceiver also being arranged to receive a second receive signal via the second antenna in the first frequency band.